DESCRIPTION (applicant's description): The extracellular matrix (ECM) of the brain is rich in hyaluronan and hyaluronan-binding molecules, suggesting that hyaluronan is the pivotal element of the brain ECM. However, being a pure polysaccharide, functional studies on hyaluronan suffered from the lack of molecular tools to directly manipulate its expression. Cloning of mammalian hyaluronan synthases has enabled to conduct studies aimed at directly addressing this issue. In this proposal, we will employ the Cre/lox-based conditional knockout technology to disrupt the hyaluronan synthase Has2 in each of the three major neural cell types, thereby generating mice in which hyaluronan synthesis is abolished specifically in respective cell types. In the first aim, we will disrupt hyaluronan synthesis in neural stem cells. Like other actively developing tissues, embryonic brain contains large amounts of hyaluronan produced by neural stem cells. We hypothesize that cell-autonomous production of hyaluronan plays a critical role in the proliferation and subsequent migration of neural stem cells. By detailed analysis of these mice, we will obtain direct evidence for the role of hyaluronan in neurogenesis in vivo. In the second aim, we will investigate the developmental role of hyaluronan in myelination by using oligodendrocyte-targeted knockout mice. During postnatal development, oligodendrocytes emerge as the major cell type that actively synthesize hyaluronan. This active hyaluronan synthesis is transient and its time window coincides with myelination. With oligodendrocyte targeted conditional knockout, we will determine whether hyaluronan plays a significant role in the formation of myelin sheaths. The third aim focuses on the role of hyaluronan in the adult brain ECM. In the adult brain, hyaluronan is concentrated in specialized structures, such as the perineuronal nets and the nodes of Ranvier, where astrocytes ensheath respective structures and elaborate ECM. We hypothesize that hyaluronan is the core component of these specialized ECM, and that the integrity of these ECM has strong impacts on biological and physiological functions of these structures. By generating astrocyte-targeted conditional knockout, we will test this hypothesis. Overall, the goal of this proposal is to obtain definitive information as to the physiological roles of hyaluronan in the CNS. The insight derived from these studies could lead to the development of hyaluronan based therapeutic approaches for neurodegenerative and demyelinating diseases.